OBJECTIVE: To investigate the structural/functional organization of a chemosensory receptor system and to determine the mechanisms by which this system regulates cellular metabolism and behavior. APPROACH: We are undertaking the purification of the cAMP receptor protein of Dictyostelium discoideum. Radioactive cAMP photoaffinity labels are being prepared in order to tag the cAMP receptor on the surface of cells. We are currently analyzing the electrophoretic patterns of membrane proteins before and after crosslinking the proteins with a variety of chemical reagents in an attempt to determine those proteins which are in physical association. Used in conjunction with the affinity labelling, we will perform a crosslinking nearest-neighbor analysis for proteins participating in the cAMP chemosensory apparatus (receptor, phosphodiesterase, etc.). We are selecting mutants by a variety of techniques (Ca45 plus 2-uptake suicide, phagocytotic suicide, resistance to cAMP killing) which may be defective in chemotactic or developmental response to cAMP and will determine possible alterations of nearest-neighbor patterns in these mutants.